Power storage device

Abstract

A cylindrical battery comprises: an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are disposed with a separator (13) therebetween; and an exterior body (16) that accommodates the electrode body (14). The negative electrode (12) has a first end and a second end in the axial direction. Current collection for the negative electrode (12) is performed from the first end side. A first mixture layer (42) of the negative electrode (12) may have a first mixture thin section (81) in which the thickness is thin at the end section on the second end side in the axial direction, and the position of formation of the first mixture thin section (81) may coincide with the position of formation of a thin section of the negative electrode (12).

Description

Power storage device

[0001] The present disclosure relates to an electricity storage device, for example, a battery or a capacitor.

[0002] A conventional energy storage device is a cylindrical secondary battery described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a bottomed cylindrical outer can that houses the electrode assembly, and a sealing body that closes the opening of the outer can. The positive electrode of the electrode assembly is electrically connected to the bottom surface of the sealing body via a positive electrode lead, and the negative electrode of the electrode assembly is electrically connected to the bottom plate portion of the outer can via a negative electrode lead.

[0003] Japanese Patent Application Laid-Open No. 2000-048825

[0004] In order to further improve the capacity and output of power storage devices and to enable stable charging and discharging in more severe environments, there is a need for further improving reliability. Therefore, an object of the present disclosure is to provide a highly reliable power storage device.

[0005] The energy storage device according to the present disclosure comprises an electrode body in which a first electrode and a second electrode are arranged with a separator interposed therebetween, and an outer casing that houses the electrode body, wherein the first electrode has a first end and a second end in a first direction, current is collected from the first end side, and the first electrode has a thin portion with a small thickness at the end on the second end side.

[0006] In addition, the energy storage device according to the present disclosure includes an electrode body in which a first electrode having a strip-shaped first core and a first composite layer arranged on the first core, a second electrode having a strip-shaped second core and a second composite layer arranged on the second core are arranged with a separator interposed therebetween, and an outer casing that houses the electrode body, wherein the first electrode has a first end and a second end in a first direction, current is collected from the first end side in the first direction, and the first core has a thin core portion with a small thickness at the end on the second end side in the first direction.

[0007] According to the present disclosure, it is easy to realize a safe and highly reliable power storage device.

[0008] 1 is an axial cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure; FIG. 2 is a perspective view illustrating the structure of an electrode body; FIG. 3(a) is a schematic plan view of a positive electrode when unfolded, and FIG. 3(b) is a schematic plan view of a negative electrode when unfolded in a strip shape; FIG. 4 is an enlarged schematic cross-sectional view of a region indicated by R in FIG. 1; FIG. 5 is a schematic plan view of a negative electrode of a reference example corresponding to FIG. 3(b); FIG. 6 is a schematic plan view of a cylindrical battery of a first modified example corresponding to FIG. 3(b); FIG. 7 is an enlarged schematic cross-sectional view of a cylindrical battery of a second modified example corresponding to FIG. 4; FIG. 8 is an enlarged schematic cross-sectional view of a cylindrical battery of a third modified example corresponding to FIG. 4; FIG. 9 is an enlarged schematic cross-sectional view of a cylindrical battery of a fourth modified example corresponding to FIG. 4; FIG. 10 is an enlarged schematic cross-sectional view of a cylindrical battery of a fifth modified example corresponding to FIG. 4; FIG. 11 is a schematic plan view of a cylindrical battery of a sixth modified example corresponding to FIG. 3(b).

[0009] Hereinafter, an embodiment of an energy storage device according to the present disclosure will be described in detail with reference to the drawings. The energy storage device according to the present disclosure may be a secondary battery using an aqueous electrolyte or a secondary battery using a nonaqueous electrolyte. The energy storage device according to the present disclosure may be a cylindrical battery having a cylindrical (e.g., bottomed cylindrical) outer can, a prismatic battery having a prismatic outer can, or a pouch-type battery having an outer body made of a laminate sheet. In these batteries, the cylindrical outer can, the prismatic outer can, and the laminate sheet form the outer body. Alternatively, the energy storage device according to the present disclosure may be a capacitor that is repeatedly charged and discharged. Below, a cylindrical secondary battery (lithium ion battery) using a nonaqueous electrolyte is illustrated as an example of an energy storage device according to one embodiment, but the energy storage device according to the present disclosure is not limited thereto.

[0010] When multiple embodiments and variations are included below, it is anticipated from the beginning that new embodiments can be constructed by appropriately combining their characteristic features. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match. In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical battery 10 is referred to as "upper," and the bottom plate portion 68 side of the outer can 16 in the axial direction is referred to as "lower." When referring to the axial direction in this specification, this axial direction refers to the axial direction of the cylindrical battery 10. The axial direction of the cylindrical battery 10 generally coincides with the height direction of the electrode assembly 14. Among the components described below, components not recited in the independent claims representing the highest concepts are optional and not required.

[0011] Fig. 1 is an axial cross-sectional view of a cylindrical battery 10 according to one embodiment of the present disclosure, and Fig. 2 is a perspective view illustrating the structure of an electrode assembly 14. As shown in Fig. 1, the cylindrical battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17.

[0012] As shown in FIG. 2 , the electrode assembly 14 has a wound structure in which a strip-shaped positive electrode 11 (an example of a sheet-like electrode) and a strip-shaped negative electrode 12 (an example of a sheet-like electrode) are wound with two strip-shaped separators 13 interposed therebetween. In this embodiment, the negative electrode 12 constitutes the first electrode, and the positive electrode constitutes the second electrode. As shown in FIG. 2 , the positive electrode 11 protrudes upward from the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes downward from the positive electrode 11 and the separator 13. The positive electrode 11 has a third exposed portion 31 on the second core 30 where the second mixture layer 32 is not provided (formed). The third exposed portion 31 extends from the inner end to the outer end of the winding direction of the strip-shaped positive electrode 11 at an upper end (an end on the fourth end side of the positive electrode) in the axial direction (first direction). In this embodiment, the second core 30 constitutes a positive electrode core, and the second mixture layer 32 constitutes a positive electrode mixture layer. The upper end of the negative electrode 12 is the end on the second end side in the axial direction of the negative electrode 12. The negative electrode 12 has a first exposed portion 41 on the first core 40 where the first mixture layer 42 is not provided, at the lower end in the axial direction (the end on the first end side of the negative electrode) from the inner end to the outer end in the winding direction of the strip-shaped negative electrode 12. In this embodiment, the first core 40 constitutes the negative electrode core, and the first mixture layer 42 constitutes the negative electrode mixture layer. The electrode body of the present disclosure does not necessarily need to wind the positive electrode and the negative electrode together with a separator. A stacked electrode body in which a plurality of sheet-type positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween may also be used.

[0013] The upper axial end of the electrode body 14 is formed by the end on the fourth end side of the positive electrode 11 and is constituted by the third exposed portion 31. The lower axial end of the electrode body 14 is formed by the end on the first end side of the negative electrode 23 and is constituted by the first exposed portion 41. The first mixture layer 42 is formed to be slightly larger than the second mixture layer 32 in order to prevent lithium precipitation. That is, the first mixture layer 42 is formed to be longer than the second mixture layer 32 in the negative electrode longitudinal direction (first longitudinal direction) and negative electrode width direction.

[0014] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0015] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0016] The positive electrode 11 includes a second core 30 and a second mixture layer 32 formed on both sides of the second core 30. The second core 30 can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The second mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to the second core 30, drying the coating, and then compressing it to form the second mixture layer 32 on both sides of the second core 30. The second mixture layer 32 may be formed on only one side of the second core. Alternatively, the second mixture layer 32 may be formed by bonding a layered sheet to the second core. A conductive adhesive containing conductive particles may be interposed between the second core 30 and the second mixture layer 32.

[0017] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0018] Examples of the conductive agent contained in the second mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the second mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, or polyethylene oxide (PEO).

[0019] The negative electrode 12 includes a first core 40 and a first mixture layer 42 formed on both sides of the first core 40. The first core 40 can be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The first mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the first core 40, drying the coating, and then compressing it to form the first mixture layer 42 on both sides of the first core 40. The first mixture layer 42 may be formed on only one side of the first core 40. Alternatively, a first mixture layer 42 already formed into a layer may be bonded to the first core 40. A conductive adhesive containing conductive particles may be interposed between the first core 40 and the first mixture layer 42.

[0020] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. The first mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0021] As in the case of the second mixture layer 32, the binder contained in the first mixture layer 42 may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like, but is preferably styrene-butadiene rubber (SBR) or a modified product thereof. In addition to SBR or the like, the first mixture layer 42 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0022] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0023] As shown in FIG. 1 , the battery 10 includes a lower current collector plate (negative electrode current collector plate) 18 made of a metal such as copper, iron, nickel, or a nickel alloy, located axially below the electrode assembly 14. The lower current collector plate 18 constitutes a first current-carrying member. In this embodiment, the lower current collector plate 18 includes a disk-shaped base 18a and a cylindrical, bottomed protrusion 18b located at the center of the base 18a and protruding axially downward. While the upper surface of the base 18a is pressed against a first exposed portion 41 that constitutes the axial lower end of the electrode assembly 14, a laser beam is irradiated from below onto the lower surface of the base 18a. This laser welding joins the first exposed portion 41 to the upper surface of the base 18a. Furthermore, a bottom plate portion 18c located at the tip of the protrusion 18b is placed on the upper surface of a bottom plate portion 68 of the outer can 16, and then a laser beam is irradiated onto the bottom plate portion 68 from below. By this laser welding, the lower current collecting plate 18 is joined to the bottom plate portion 68 and electrically joined to the outer casing 16 .

[0024] In the above description, the first exposed portion 41 is electrically connected to the outer can 16 via the lower current collector plate 18. However, the negative electrode may be electrically connected to the outer can 16 via one or more negative electrode leads protruding from the lower end of the electrode assembly. Alternatively, in addition to or instead of being electrically connected to the outer can 16 via one or more negative electrode leads, the negative electrode may be electrically connected to the outer can 16 by contacting an exposed portion of the negative electrode core provided on the outermost periphery of the electrode assembly with the inner circumferential surface of the outer can 16. Alternatively, the first exposed portion 41 may be directly bonded to the bottom plate portion 68 of the outer can 16 using a laser or the like. The first exposed portion 41 may be bonded to the lower current collector plate 18 in a radially bent state. Furthermore, the first exposed portions 41 may be bonded to the lower current collector plate 18 in a state in which the first exposed portions 41 aligned radially overlap each other.

[0025] The battery 10 includes an upper current collector 19 (positive electrode current collector) made of a metal such as aluminum or an aluminum alloy, located axially above the electrode assembly 14. The upper current collector 19 constitutes a second current-carrying member. The upper current collector 19 has a base 19a electrically connected to the positive electrode 11 and a through-hole 19b located at the center of the base 19a. A spacer 37 made of an insulating material that prevents connection between the upper current collector 19 and the outer can 16 is provided between the base 19a and the outer can 16. While the lower surface of the base 19a is pressed against a third exposed portion 31 that constitutes the upper end of the electrode assembly 14, a laser beam is irradiated from above onto the upper surface of the base 19a. This laser welding bonds the third exposed portion 31 to the lower surface of the base 19a.

[0026] The tip side of the third exposed portion 31 may be bent in the radial direction and joined to the upper current collecting plate 19. Furthermore, the third exposed portions 31 may be joined to the upper current collecting plate 19 in a state where the third exposed portions 31 aligned in the radial direction overlap each other. Alternatively, a positive electrode lead (not shown) joined to the positive electrode 11 may be joined to the upper surface of the base 19a after passing through the through hole 19b.

[0027] The sealing body 17 is composed of a gasket 28 and a terminal cap 27. The terminal cap 27 is composed of metal. The terminal cap 27 has a disk-shaped base 27a and a protrusion 27b, and the protrusion 27b is composed of, for example, a cylindrical protrusion. The base 27a of the terminal cap 27 may be connected to the upper surface of the base 19a of the upper current collector plate 19 via a strip-shaped lead 55. The lead 55 is composed of a conductive material, for example, a metal. Methods for joining the lead 55 to the base 27a and the base 19a include welding. For example, the terminal cap 27 and the upper current collector plate 19 are electrically connected via the lead 55 by laser welding.

[0028] The outer can 16 is generally made of a metal primarily composed of iron, such as nickel-plated iron. The outer can 16 may also be made of a metal primarily composed of aluminum or the like. The outer can 16 has a cylindrical portion 65 and a bottom plate portion 68. The cylindrical portion 65 includes an annular groove portion 35 and an annular shoulder portion 38. The groove portion 35 is formed by spinning a portion of the cylindrical portion 65 to recess it radially inward around the entire circumferential direction. The shoulder portion 38 is formed when the upper end of the cylindrical portion 65 is bent radially inward and crimped onto the peripheral edge portion 48 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 65.

[0029] The peripheral edge 48 of the terminal cap 27 is crimped between the shoulder 38 and the groove 35 via the gasket 28, thereby fixing the sealing body 17 to the outer can 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer can 16 from the sealing body 17. The gasket 28 is made of, for example, polyolefin. The groove 35 is formed at a position a predetermined distance from the upper end of the outer can 16. The predetermined length is, for example, a length equivalent to 1 to 20% of the axial length of the outer can 16. The gasket 28 is compressed by the shoulder 38. The gasket 28 has a protrusion 28a that protrudes radially inward from between the shoulder 38 and the sealing body 17.

[0030] A thin, easily breakable portion 69 is provided on the bottom plate portion 68. The easily breakable portion 69 is provided, for example, by stamping a circle or a C-shape on the underside of the bottom plate portion 68. When the battery 10 generates abnormal heat and the internal pressure of the battery 10 rises to a predetermined pressure, the easily breakable portion 69 breaks and gas is released from the bottom plate portion 68. This gas release prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby increasing the safety of the battery 10.

[0031] The battery 10 further includes an annular metal plate 80 and an annular insulating plate 82 made of an insulating material. The metal plate 80 has an annular portion 80a extending generally in the radial direction and a cylindrical portion 80b extending downward from one radial end of the annular portion 80a. The tip of the cylindrical portion 80b may be engaged with the groove 35. The annular portion 80a is joined to the upper surface of the shoulder portion 38.

[0032] The terminal cap 27, whose third exposed portion 31 is electrically connected to the upper current collector plate 19 via the lead 55, serves as the positive electrode terminal, and the metal plate 80, whose first exposed portion 41 is electrically connected to the lower current collector plate 18 via the outer casing 16, serves as the negative electrode terminal. The metal plate 80 is electrically connected to a current collector plate (not shown) that connects multiple batteries 10 in series or parallel, for example, using the tongue portion (lead) of the current collector plate. In this manner, multiple batteries 10 can be easily electrically connected to the current collector plate.

[0033] The insulating plate 82 is interposed between the metal plate 80 and the sealing member 17 to insulate the metal plate 80 from the sealing member 17. The radially outer peripheral edge of the insulating plate 82 may be located above the protruding portion 28a of the gasket 28 and contact the gasket 28. In this manner, the gasket 28 and the insulating plate 82 reliably insulate the metal plate 80 from the sealing member 17. A cylindrical portion 83 is provided around the periphery of the hollow portion of the insulating plate 82, covering the outer peripheral surface of the protruding portion 27b of the terminal cap 27. The cylindrical portion 83 is connected to the radially inner end of the plate-shaped base of the insulating plate 82. Note that the cylindrical battery 10 does not necessarily have to have the metal plate 80 and the insulating plate 82.

[0034] FIG. 3( a) is a schematic plan view of the positive electrode 11 when unwound, and FIG. 3( b) is a schematic plan view of the negative electrode 12 when unwound into a strip shape. FIG. 4 is an enlarged schematic cross-sectional view of the region indicated by R in FIG. 1 . As shown in FIG. 3( a), the positive electrode 11 has a resin layer (insulating layer) 33 on both the outer and inner surfaces of the winding, in which an insulating resin such as polyvinylidene fluoride (PVdF) is disposed on the second core 30. The resin layer 33 is provided to prevent short-circuiting between the positive electrode 11 and the negative electrode 12. The resin layer 33 is provided on both sides of the positive electrode 11, from the inner end of the winding to the outer end of the winding in the winding direction. The resin layer 33 is disposed between the third exposed portion 31 and the second mixture layer 32 in the width direction of the positive electrode. Note that this resin layer may contain an electrically insulating metal oxide such as alumina.

[0035] As shown in FIG. 4 , on each of the inner and outer winding surfaces of the positive electrode 11, the second material mixture layer 32 has a second material mixture thin portion 71 with a small thickness at the end portion near the fourth end (the end portion near the second end). The second material mixture thin portion 71 is formed at substantially the same position in the positive electrode width direction on the inner and outer winding surfaces of the positive electrode 11. The second material mixture thin portion 71 extends from a portion of the second material mixture layer 32 with a substantially constant thickness toward the fourth end in the positive electrode width direction and is smaller than the substantially constant thickness portion. The second material mixture thin portion 71 gradually decreases in thickness toward the tip near the fourth end. The second material mixture layer thick portion may be connected to the substantially constant thickness portion via a step portion and located closer to the second end than the substantially constant thickness portion. The second material mixture layer thick portion may have a substantially constant thickness that is smaller than the substantially constant thickness portion. In the electricity storage device of the present disclosure, the second mixture layer thin portion may be omitted.

[0036] As shown in FIG. 3( a), on each of the inner and outer winding surfaces of the positive electrode 11, the second mixture thin-walled portion 71 is provided at the same location on the end portion on the fourth end side in the positive electrode width direction from the inner winding end to the outer winding end in the positive electrode longitudinal direction, which is an example of the second longitudinal direction. The second mixture thin-walled portion 71 can be provided by reducing the amount of positive electrode slurry applied to a predetermined location on the end portion on the fourth end side in the positive electrode width direction on each of the inner and outer winding surfaces of the positive electrode 11 so as to correspond to the thickness of the second mixture thin-walled portion 71. Alternatively, the second mixture thin-walled portion 71 can be provided by increasing the pressure applied to a predetermined location on the end portion on the fourth end side in the positive electrode width direction during rolling on each of the inner and outer winding surfaces of the positive electrode 11. Such rolling can be performed by providing an annular protrusion on a rolling roller at a location corresponding to the predetermined location on the end portion on the fourth end side in the positive electrode width direction.

[0037] As shown in FIG. 4 , on each of the inner and outer winding surfaces of the negative electrode 12, the first material mixture layer 42 includes a first material mixture thin portion 81 having a small thickness at an end (upper end) on the second end side in the first direction (coincident with the negative electrode width direction). The first material mixture thin portion 81 is formed at substantially the same position in the negative electrode width direction on the inner and outer winding surfaces of the negative electrode 12. The location of the negative electrode 12 where the first material mixture thin portion 81 is provided corresponds to the thin portion of the negative electrode 12 with a small thickness. As shown in FIG. 3( b ), on each of the inner and outer winding surfaces of the negative electrode 12, the first material mixture thin portion 81 is provided at the same location on the end on the second end side in the negative electrode width direction from the inner winding end to the outer winding end in the first longitudinal direction (negative electrode longitudinal direction).

[0038] The first mixture thin-walled portion 81 can be provided at a predetermined location on the end portion on the second end side in the negative electrode width direction by reducing the amount of negative electrode slurry applied to a predetermined location on each of the inner and outer winding surfaces of the negative electrode 12. Alternatively, the first mixture thin-walled portion 81 can be provided by increasing the pressure applied to a predetermined location on the end portion on the second end side in the negative electrode width direction during rolling of each of the inner and outer winding surfaces of the negative electrode 12. Such rolling can be performed by providing an annular protrusion on a rolling roller at a location corresponding to the rolling of the predetermined location on the end portion on the second end side in the negative electrode width direction.

[0039] The first mixture thin-walled portion 81 is located axially above the second mixture thin-walled portion 71 (the axial end portion of the second mixture layer). That is, the first mixture thin-walled portion 81 is formed in a non-overlapping portion of the first mixture layer 42 that does not overlap with the second mixture layer 32, and is formed in a non-facing portion extending outward from the second mixture layer 32 in the first direction. This non-overlapping portion is located axially outward from the second mixture layer. However, it is not necessarily prohibited to form a first mixture thin-walled portion in an overlapping portion of the first mixture layer that overlaps with the second mixture layer. In this way, a decrease in battery capacity is suppressed. The first mixture thin-walled portion 81 may be provided in a region facing the second mixture layer 32. The first mixture thin-walled portion 81 may also be formed to extend in a direction intersecting the axial direction and the direction in which the positive electrode and the negative electrode oppose each other (e.g., the longitudinal direction of the negative electrode 12).

[0040] Next, the effects achieved by providing a first material mixture thin portion 81 (corresponding to the thin portion of the negative electrode 12) on at least a portion of the upper end of the negative electrode 12 will be described. When the battery 10 is repeatedly charged and discharged many times, the positive electrode 11 and the negative electrode 12 may expand in the axial direction (height direction of the electrode body). Expansion and contraction during charging and discharging occur in the negative electrode 12. The negative electrode 12 expands in the radial and axial directions during charging. It is presumed that the axial expansion of the negative electrode 12 occurs due to the expansion of the negative electrode during charging.

[0041] 5, that is, a schematic plan view of the negative electrode 712 of the reference example corresponding to FIG. 3(b), if the negative electrode 712 has a simple rectangular shape, the separator 13 insulating the positive electrode 11 from the negative electrode 712 may be damaged at an upper end (edge) 712a of the negative electrode 712 as the negative electrode 712 stretches in the negative electrode width direction, and the negative electrode 712 may come into contact with the third exposed portion 31 due to damage to the separator 13. On the other hand, if the exposed portion of the positive electrode 11 is bent and the resin layer formed on this bent exposed portion faces the negative electrode in the axial direction, the negative electrode 12, which has the resin layer stretched, may be damaged.

[0042] In contrast, in the battery 10 of the present disclosure, the negative electrode 12 includes a first material mixture thin-wall portion 81 at its upper end that extends from the inner end of the winding to the outer end of the winding in the longitudinal direction of the negative electrode, thereby reducing the rigidity of the upper end (edge) of the negative electrode 12. Therefore, even if the negative electrode 12 elongates in the axial direction and the edge of the negative electrode 12 presses against the separator 13, the edge of the negative electrode 12 is likely to bend in the direction indicated by arrow A in Figure 4 due to the reaction force received from the separator 13 or the resin layer, thereby preventing damage to the separator 13 or the resin layer. This prevents contact between the positive electrode 11 and the negative electrode 12, thereby improving the reliability of the battery 10.

[0043] Furthermore, since the second mixture layer 32 of the positive electrode 11 has a second mixture thin portion 71 with a small thickness in at least a portion of the positive electrode width direction at the end (upper end) on the second end side in the axial direction, the amount of lithium ions released from the second mixture layer 32 during charging is reduced. Therefore, even if the amount of lithium ions that can be received at the upper end of the negative electrode 12 during charging is reduced by providing the first mixture thin portion 81 in at least a portion of the negative electrode width direction at the upper end of the negative electrode 12, lithium can be prevented from being deposited on the surface of the negative electrode 12. Therefore, deterioration of the battery 10 during charging can be suppressed.

[0044] The present disclosure is not limited to the above-described embodiment and its modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0045] For example, in the above embodiment, the first material mixture layer 42 of the negative electrode 12 includes, at the end (upper end) on the second end side in the axial direction, a first material mixture thin portion 81 having a small thickness from the inner end to the outer end in the longitudinal direction of the negative electrode. However, the first material mixture thin portion does not have to be provided over the entire area from the inner end to the outer end in the longitudinal direction of the negative electrode, and may be provided locally in the longitudinal direction of the negative electrode.

[0046] For example, depending on the specifications, the axial elongation of the positive and negative electrodes may be significant on the inner side of the electrode assembly in the winding direction. In this case, as shown in Figure 6, i.e., the schematic plan view of the cylindrical battery 110 of the first modification corresponding to Figure 3(b), a first composite thin-walled portion 181 may be provided only on the inner side of the winding direction at the upper end of the negative electrode 112. In this case, damage to the separator 13 can be effectively suppressed by forming a small area of ​​the first composite thin-walled portion.

[0047] Furthermore, although the case where the third exposed portion 31 provided at the upper end (end on the fourth end side) of the positive electrode 11 is joined to the sealing body 17 has been described, the positive electrode may be joined to the sealing body using one or more positive electrode leads. One or more first material mixture thin-walled portions may be locally provided around a region that radially faces one or more positive electrode leads at the upper end (end on the second end side) of the negative electrode, with the separator interposed between them. In this case, if at least a portion of the first material mixture thin-walled portion is provided in a position that radially overlaps the positive electrode lead with the separator interposed between them, contact between the negative electrode and the positive electrode lead can be effectively suppressed.

[0048] In addition, the case where the second mixture layer 32 of the positive electrode 11 has a second mixture thin portion 71 with a small thickness in at least a portion in the positive electrode width direction at the end (upper end) on the second end side in the axial direction has been described. However, as shown in Figure 7, that is, the enlarged schematic cross-sectional view of a cylindrical battery 210 of a second modified example corresponding to Figure 4, the second mixture layer 232 of the positive electrode 211 does not have to have a second mixture thin portion.

[0049] The above description also illustrates a case in which the first mixture layer 42 of the negative electrode 12 has a first mixture thin-walled portion 81 with a small thickness in at least a portion of the negative electrode width direction at the end (upper end) on the second end side in the axial direction. However, as shown in FIG. 8 , i.e., an enlarged schematic cross-sectional view of a cylindrical battery 310 of a third modified example corresponding to FIG. 4 , the first mixture layer 342 of the negative electrode 312 does not necessarily have a first mixture thin-walled portion in the end (upper end) on the second end side in the axial direction. Instead, the first core 340 of the negative electrode 312 may have a first core thin-walled portion 391 with a small thickness in at least a portion of the negative electrode width direction at the end (upper end) on the second end side in the axial direction. The first core thin-walled portion 391 may extend in a direction intersecting the first direction. The first core 340 may have a non-facing portion extending outward from the second mixture layer in the first direction, and the first core thin-walled portion 391 may be formed in the non-facing portion.

[0050] In this case, the thickness of the negative electrode 312 at the position where the first core thin portion 391 is formed in the negative electrode width direction may be approximately the same as the thickness of the negative electrode 312 at other positions in the negative electrode width direction. Because the rigidity per unit volume of the first core 340 is greater than the rigidity per unit volume of the first mixture layer 342, even if done in this way, the rigidity of the first core thin portion 391 at the position where it is formed in the negative electrode width direction can be reduced.

[0051] Alternatively, as shown in Figure 9, i.e., an enlarged schematic cross-sectional view corresponding to Figure 4 of the cylindrical battery 410 of the fourth modified example, the thickness of the negative electrode 412 at the formation position in the negative electrode width direction of the first core thin portion 491 may be thinner by the same amount as the thickness of the first core 440 at that formation position.

[0052] Furthermore, as shown in Figure 10, i.e., the enlarged schematic cross-sectional view corresponding to Figure 4 of a cylindrical battery 510 of the fifth modified example, the first mixture layer 542 of the negative electrode 512 may have a first mixture thin-walled portion 581 having a small thickness in at least a portion of the negative electrode width direction at the end (upper end) on the second end side in the axial direction. The first core 540 of the negative electrode 512 may also have a first core thin-walled portion 591 having a small thickness in at least a portion of the negative electrode width direction at the end (upper end, non-overlapping portion that does not overlap with the second mixture layer in a direction intersecting the direction in which the positive electrode and negative electrode oppose each other) on the second end side in the axial direction. The first core thin-walled portion 591 may be formed in an overlapping portion of the first core 540 that overlaps with the second mixture layer in a direction intersecting the direction in which the positive electrode and negative electrode oppose each other.

[0053] 10 , the position where the first material mixture thin portion 581 is formed in the negative electrode width direction may substantially coincide with the position where the first substrate thin portion 591 is formed in the negative electrode width direction, or the position where the first material mixture thin portion is formed in the negative electrode width direction may differ from the position where the first substrate thin portion is formed in the negative electrode width direction. When the position where the first material mixture thin portion 581 is formed in the negative electrode width direction substantially coincides with the position where the first substrate thin portion 591 is formed in the negative electrode width direction, the rigidity of the negative electrode 512 is significantly reduced locally, and damage to the separator 13 or the resin layer due to elongation of the negative electrode 512 can be effectively suppressed.

[0054] Furthermore, the case where the entire upper end of the negative electrode 12 is included in the first mixture layer 42 and the upper end of the negative electrode 12 includes the first mixture thin portion 81 has been described. However, as shown in FIG. 11 , i.e., a schematic plan view of a cylindrical battery 610 of a sixth modified example corresponding to FIG. 3( b), the negative electrode 612 may have a second exposed portion 639 extending in the first longitudinal direction at the upper end. The first core thin portion 691 may be provided in the second exposed portion 639. This further reduces the rigidity of the upper end (edge) of the negative electrode 612, thereby further preventing the edge of the negative electrode 612 from damaging the separator 13.

[0055] The case where the first electrode is a negative electrode and the second electrode is a positive electrode has been described. However, the first electrode may be a positive electrode and the second electrode may be a negative electrode. The positive electrode may also expand in the height direction (axial direction) of the electrode body due to the following phenomenon. Specifically, expansion and contraction during charging and discharging occurs in the negative electrode, and the negative electrode expands in the radial and axial directions during charging. During charging, the radial expansion of the negative electrode increases the radial surface pressure within the electrode body. Therefore, the axial expansion of the negative electrode pulls the positive electrode in the height direction of the electrode body, making it more likely to expand in the axial direction.

[0056] On the other hand, during discharge, the radial contraction of the negative electrode reduces the radial surface pressure within the electrode body, preventing the positive electrode from being pulled back by the contraction of the negative electrode in the height direction of the electrode body. As a result, repeated charge and discharge may cause the positive electrode to elongate in the height direction of the electrode body. In view of this phenomenon, in this case, at least one of a thin cathode mixture portion (first thin mixture portion) and a thin cathode substrate portion (first thin substrate portion) may be provided in at least a portion of the axial lower end (corresponding to the end of the second end) of the positive electrode constituting the first electrode. In this case, contact between the lower end of the positive electrode and the lower end of the negative electrode due to axial expansion of the positive electrode can be suppressed.

[0057] Furthermore, the structure of the sealing body is not limited to the structure of the embodiment. The sealing body may have a laminated structure including two rupture plates (a lower valve body and an upper valve body), and a convex terminal cap may be present to cover the rupture plate. Alternatively, the sealing body may be composed of only a rupture plate, or may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in this order from the electrode body side. In these cases, the bottom plate portion of the outer can does not need to have a thin, easily breakable portion.

[0058] Furthermore, the lower end of the negative electrode does not necessarily have to be connected to the outer can. A through-hole may be formed in the bottom plate of the outer can, and the negative electrode may be connected to a terminal inserted through the through-hole. Furthermore, while the battery 10 has been described as including a lower current collector 18 and an upper current collector 19, the cylindrical battery may not include one or both of the first current-carrying member and the second current-carrying member. Furthermore, although the positive electrode 11 has been described as including a resin layer 33, the positive electrode 11 may not include a resin layer.

[0059] The power storage device according to the present disclosure may also have the following configurations. Configuration 1: A power storage device including an electrode assembly in which a first electrode and a second electrode are arranged with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the first electrode has a first end and a second end in a first direction, current collection for the first electrode is performed from the first end side, and the first electrode has a thin-walled portion with a small thickness at an end portion on the second end side. Configuration 2: The power storage device according to Configuration 1, wherein the first electrode has a strip-shaped first core and a first mixture layer disposed on the first core, and the second electrode has a strip-shaped second core and a second mixture layer disposed on the second core, and the first mixture layer has a first mixture thin-walled portion with a small thickness at an end portion on the second end side in the first direction. Configuration 3: The power storage device according to Configuration 1 or 2, wherein the thin-walled portion extends in a direction intersecting the first direction.

[0013] Aspect 4: The power storage device according to Aspect 2, wherein the first electrode has a non-facing portion extending outward from the second mixture layer in the first direction, and the thin portion is formed in the non-facing portion. Aspect 5: The power storage device according to Aspect 2, comprising: an electrode assembly including a first electrode having a sheet-like first core and a first mixture layer disposed on the first core, and a second electrode having a sheet-like second core and a second mixture layer disposed on the second core, arranged with a separator interposed therebetween; and an exterior housing that houses the electrode assembly, wherein the first electrode has a first end and a second end in the first direction, current is collected from the first end side in the first direction, and the first core has a thin core portion with a small thickness at an end portion on the second end side in the first direction. Aspect 6: The power storage device according to Aspect 5, wherein the thin core portion extends in a direction intersecting the first direction. Configuration 7: The electricity storage device according to Configuration 5 or 6, wherein the first core has a non-facing portion extending outward from the second mixture layer in the first direction, and the thin-walled core portion is formed in the non-facing portion.Configuration 8: The electricity storage device according to Configuration 2, wherein the second mixture layer has a second thin-walled mixture portion having a smaller thickness at an end portion on the second end side in the first direction.Configuration 9: The electricity storage device according to Configuration 2, wherein the first core has a thin-walled core portion having a smaller thickness at an end portion on the second end side in the first direction.10: The power storage device according to any one of the preceding embodiments, further comprising a first current-carrying member electrically connected to the first electrode, wherein an end of the first electrode on the first end side has a first exposed portion extending in the first longitudinal direction of the first electrode, where the first mixture layer is not formed, but where the first core is exposed, and the first current-carrying member and the first exposed portion are joined. 11: The power storage device according to any one of the preceding embodiments, further comprising: a first current-carrying member electrically connected to the first electrode, wherein an end of the first electrode on the first end side has a second exposed portion extending in the first longitudinal direction of the first electrode, where the first mixture layer is not formed, but where the first core is exposed, and the second exposed portion is joined. 12: The power storage device according to Configuration 2, 4, 5, 6, 7, 8, 9, 10, or 11, further including a second current-carrying member electrically connected to the second electrode, wherein in the first direction, the second electrode has a third end disposed on the side of the first end and a fourth end disposed on the side of the second end, the second electrode has a third exposed portion at an end on the fourth end side, extending in a second longitudinal direction of the second electrode, where the second mixture layer is not formed, but where the second core is exposed, and the second current-carrying member and the third exposed portion are joined. 13: The power storage device according to Configuration 12, wherein an insulating layer having electrical insulation properties is formed between the third exposed portion and the second mixture layer.

[0060] 10,110,210,310,410,510,610 Cylindrical battery, 11,211 Positive electrode, 12,112,312,412,512,612 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer can, 16 Outer can, 17 Sealing body, 18 Lower current collector plate, 18a Base, 18b Protruding portion, 18c Bottom plate portion, 19 Upper current collector plate, 19a Base, 19b Through hole, 23 Negative electrode, 27 Terminal cap, 27a Base, 27b Protruding portion, 28 Gasket, 28a Protruding portion, 30 Second core (positive electrode core), 31 Third exposed portion, 32,232 Second mixture layer (positive electrode mixture layer), 33 Resin layer, 35 Groove portion, 37 Spacer, 38 Shoulder portion, 40, 340, 440, 540 First core (negative electrode core) 41 First exposed portion, 42, 342, 542 First mixture layer (negative electrode mixture layer), 48 Peripheral edge portion, 55 Lead, 65 Cylindrical portion, 68 Bottom plate portion, 69 Easily breakable portion, 71 Second mixture thin portion (positive electrode mixture thin portion) 80 Metal plate, 80a Annular portion, 80b Cylindrical portion, 81, 181, 581 First mixture thin portion (negative electrode mixture thin portion) 82 Insulating plate, 83 Cylindrical portion, 391, 491, 591, 691 First core thin part (negative electrode core thin part) 639 Second exposed part.

Claims

1. An electricity storage device comprising: an electrode assembly in which a first electrode and a second electrode are arranged with a separator between them; and an exterior housing that houses the electrode assembly, wherein the first electrode has a first end and a second end in a first direction, current collection for the first electrode is performed from the first end side, and the first electrode has a thin portion with a small thickness at the end on the second end side.

2. The energy storage device according to claim 1, wherein the first electrode has a strip-shaped first core and a first mixture layer arranged on the first core, and the second electrode has a strip-shaped second core and a second mixture layer arranged on the second core, and the first mixture layer has a first mixture thin-walled portion, which is the thin-walled portion with a smaller thickness, at an end on the second end side in the first direction.

3. The power storage device according to claim 1, wherein the thin-walled portion extends in a direction intersecting the first direction.

4. The energy storage device according to claim 2, wherein the first electrode has a non-facing portion extending outward beyond the second mixture layer in the first direction, and the thin portion is formed in the non-facing portion.

5. An energy storage device comprising: an electrode body in which a first electrode having a sheet-like first core and a first mixture layer disposed on the first core, and a second electrode having a sheet-like second core and a second mixture layer disposed on the second core are arranged with a separator in between; and an exterior body that houses the electrode body, wherein the first electrode has a first end and a second end in a first direction, current is collected from the first end side in the first direction, and the first core has a thin core portion with a small thickness at the end on the second end side in the first direction.

6. The electricity storage device according to claim 5, wherein the core thin portion extends in a direction intersecting the first direction.

7. The energy storage device according to claim 5, wherein the first core has a non-facing portion extending outward beyond the second mixture layer in the first direction, and the thin-walled core portion is formed in the non-facing portion.

8. The energy storage device according to claim 2, wherein the second mixture layer has a second mixture thin portion having a small thickness at an end portion on the second end side in the first direction.

9. The energy storage device according to claim 2, wherein the first core has a thin core portion having a small thickness at an end on the second end side in the first direction.

10. An electricity storage device according to claim 2, 4, 5, 6, 7, 8 or 9, further comprising a first current-carrying member electrically connected to the first electrode, wherein a first exposed portion is formed at an end of the first electrode on the first end side, extending in the first longitudinal direction of the first electrode, where the first mixture layer is not formed, but where the first core is exposed, and the first current-carrying member and the first exposed portion are joined.

11. The energy storage device according to claim 2, 4, 5, 6, 7, 8 or 9, wherein the first electrode has a second exposed portion at the end on the second end side that extends in the first longitudinal direction of the first electrode and where the first mixture layer is not formed, but where the first core is exposed, and a thin core portion having a small thickness is formed in the second exposed portion.

12. The electricity storage device according to claim 2, 4, 5, 6, 7, 8 or 9, further comprising a second current-carrying member electrically connected to the second electrode, wherein in the first direction, the second electrode has a third end arranged on the side of the first end and a fourth end arranged on the side of the second end, and the second electrode has, at an end on the fourth end side, a third exposed portion extending in a second longitudinal direction of the second electrode where the second mixture layer is not formed but where the second core is exposed, and the second current-carrying member and the third exposed portion are joined.

13. The electricity storage device according to claim 12, wherein an insulating layer having electrical insulating properties is formed between the third exposed portion and the second mixture layer.

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